Compressors provided in turbo refrigerators employ the forced-circulation method in which lubricating oil is forcedly supplied by a lubricating oil pump from a lubricating oil tank to a gear and bearing that drive the compressor. Because of this, due to a pressure difference (oil-supply differential pressure) between the pressure at the outlet of the lubricating oil pump and the pressure inside the lubricating oil tank during operation of the turbo refrigerator, some of the lubricating oil inside the lubricating oil tank is sucked into the compressor, causing the level of lubricating oil in the lubricating oil tank to drop.
When the level of lubricating oil in the lubricating oil tank drops in this way, the oil supply differential pressure between the pressure at the outlet of the lubricating oil pump and the pressure inside the lubricating oil tank ends up being reduced, and there is a risk of damage to the compressor. Because the lubricating oil sucked in by the compressor is guided to a condenser together with refrigerant, the lubricating oil adheres to a heat exchanger portion in the condenser, causing a reduction in heat transfer.
A method for recovering the lubricating oil sucked into the compressor and mixed with the refrigerant involves using a shell-and-tube condenser and recovering the lubricating oil as drainage, and providing an oil mist separator tank at a discharge side of the compressor for performing separation and recovery of the lubricating oil that is mixed with the refrigerant.
Patent Literature 1 and Patent Literature 4 disclose inventions directed to cyclone-type oil mist separators, and Patent Literature 2 and Patent Literature 3 disclose inventions directed to demister-type oil mist separators.
Patent Literature 5 discloses making finer droplets of lubricating oil by using a double-flow nozzle, thereby improving the cooling effect of the refrigerant during the compression process in the compressor with a supply of lubricating oil.
The cyclone-type oil mist separator tank will be described here using FIGS. 3A to 4F.
FIG. 3A is a longitudinal sectional view showing, in outline, the configuration of a cyclone-type oil mist separator tank in the related art, and FIG. 3B is a lateral sectional view showing, in outline, the configuration thereof.
An oil mist separator tank 100 includes a cylindrical tank body 101 and end plates 102 at both ends of the tank body 101. A core 103 passes through along the center axis of the tank body 101. By rotating the oil mist separator tank 100 about this core 103, the lubricating oil that is mixed with the refrigerant is centrifugally separated. An oil collecting demister (not illustrated) is provided at an inner wall of the tank body 101, where the centrifugally separated lubricating oil is trapped so as to be prevented from being redispersed.
A refrigerant inflow pipe 104 through which the refrigerant, mixed with the lubricating oil, flows in is provided in the tank body 101 near one of the end plates 102a provided at both ends of the tank body 101, and a refrigerant outflow pipe 105 through which the refrigerant, from which the lubricating oil has been separated, flows out to the outside is provided in the tank body 101 near the other end plate 102b. An oil drain hole, which is not illustrated, is provided in the tank body 101 so that the trapped lubricating oil can be discharged.
Tangential velocity vectors inside an oil mist separator tank 100 with such a configuration will be described using FIGS. 4A to 4F.
FIGS. 4A to 4F show tangential velocity vector diagrams inside the oil mist separator tank, where FIG. 4A is a schematic view of the oil mist separator tank shown in FIG. 3A, and FIGS. 4B to 4F show tangential velocity vector diagrams in cross-sections at part F-F to part J-J in FIG. 4A.
The tangential velocity vector diagrams in each of the cross-sections in FIGS. 4B to 4F show cases where the refrigerant that has flowed into the oil mist separator tank 100 from the refrigerant inflow pipe 104 is divided into five parts, from the upstream side to the downstream side, in this order, in the axial direction of the oil mist separator tank 100.
As shown in FIG. 4B, the tangential velocity vectors in the cross-section F-F in the oil mist separator tank 100, on the extension of the center axis of the refrigerant inflow pipe 104, are densely and substantially uniformly distributed so as to point in the extending direction of the center axis of the refrigerant inflow pipe 104, in the space (at the left side in FIG. 4B) formed between the core 103 (see FIG. 3B) and the tank body 101 through which the refrigerant inflow pipe 104 passes.
The oil-containing refrigerant that has flowed into the oil mist separator tank 100 from the refrigerant inflow pipe 104 flows in the direction of the extension line of the center axis of the refrigerant inflow pipe 104 and collides with the inner wall of the tank body 101 which exists in front thereof, causing the flow direction to turn so as to go along the inner wall of the tank body 101. Of the refrigerant whose flow direction has turned, the velocity of the refrigerant along the inner wall of the tank body 101 becomes faster than the velocity of the refrigerant that flows near the outer wall of the core 103, causing swirling. This is shown, in FIG. 4B, by the fact that the velocity vectors near the inner wall of the tank body 101 become denser than the velocity vectors near the outer wall of the core 103.